Hi Gabriele, Adrian, Tadeusz, Aidan,
during testing of my algif_aead patch with the different GCM implementations I
am able to trigger a kernel crash from user space using __driver-gcm-aes-
aesni.
As I hope that algif_aead is going to be included, unprivileged userspace
would then reliably crash the kernel -- with the current kernel code,
userspace has no interface to trigger the issue.
Looking into the kernel code I think I see where the issue is. The crash
happens when setkey is invoked. The kernel crypto API defines setkey as the
following:
static inline int crypto_aead_setkey(struct crypto_aead *tfm, const u8 *key,
unsigned int keylen)
{
struct aead_tfm *crt = crypto_aead_crt(tfm);
return crt->setkey(crt->base, key, keylen);
}
This means that the kernel crypto API expects that ciphers always implement a
setkey callback.
However, __driver-gcm-aes-aesni does not implement a setkey:
.aead = {
.encrypt = __driver_rfc4106_encrypt,
.decrypt = __driver_rfc4106_decrypt,
},
As I am not sure what the purpose of __driver-gcm-aes-aesni is (only a backend
for RFC4106 GCM or a regular cipher), I did not yet create a patch. IMHO there
are two solutions:
- either create a valid setkey callback so that a key is set
- or create a noop setkey that returns -EOPNOTSUPP which effectively disables
that cipher for regular consumption.
Note, if it is only a backend for the RFC4106 implementation, may I ask why
__driver-gcm-aes-aesni is implemented as a separate cipher that is registered
with the kernel crypto API?
--
Ciao
Stephan
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